The significant temperature sensitivity of semiconductor lasers limits their use in high temperature environments, such as those often encountered in aerospace and military applications. Even in a stable temperature environment, heating due to the operation of a semiconductor laser can produce enough temperature increase to affect laser performance. To avoid heating problems, a thermoelectric cooler is often packaged with a semiconductor laser. However, this approach increases the size, power consumption, and weight of the device. In addition, commercially available thermoelectric coolers are not certified for long term reliability, or for use in environments subject to vibration. The inclusion of a thermoelectric cooler can therefore reduce the reliability of a semiconductor laser device.
It has previously been appreciated that the heating that occurs during operation of a semiconductor laser can be reduced by lowering the threshold current density of the device. For gallium arsenide (GaAs) based semiconductor lasers, it has also been noted that designs with quantum well active layers have high temperature characteristics that are superior to those that use more conventional (bulk) active layer designs. However, there has been a large variation in the results obtained by different workers on this point. Finally, it has also been noted that for quantum well, gallium arsenide based lasers, straining the active layer can produce an increase in the reliability of the device and lower threshold current densities. However, it has previously been unclear how these different observations were interrelated, and how they could be used to produce more reliable semiconductors lasers.